The invention relates to a family of novel compositions which exhibit excellent properties when spray-dried, as well as novel methods of spray-drying compositions. In particular, the invention provides methods for spray-drying catalyst compounds, in which the resulting spray-dried catalyst materials exhibit properties which are desirable for use in catalysis, as well as compositions used in such spray-drying methods.
A number of methodologies used for delivering catalysts to reactors require that the catalyst be supported, e.g., by impregnating the catalyst on an inert carrier such as silica. Impregnating a catalyst on a support has often been found to cause a significant decrease in catalyst activity. In addition, large particles ( greater than 25 micrometers) of the support material, e.g., silica, have frequently been found in the finished polymer product, where they may adversely affect polymer properties. This has been observed in film applications where unexploded silica particles appear as defects or gels.
Spray-drying techniques have been applied to catalyst compositions, e.g., as an alternative to impregnating the catalyst on a support. For example, U.S. Pat. No. 5,290,745 discloses preparing a solution of titanium trichloride and magnesium dichloride in an electron donor compound (e.g., tetrahydrofuran), admixing the solution with a filler, heating the resulting slurry to a temperature as high as the boiling point of the electron donor compound; and then atomizing the slurry by means of a suitable atomizing device to form discrete spherically shaped particles.
However, it has been found that it is very difficult to closely control morphology of the product obtained by spray-drying of catalyst compositions. In addition, it has been found that it is very difficult to consistently obtain spray-dried catalyst particles which have a high degree of products having uniform sizes and high degrees of sphericity. These problems have been particularly troublesome with regard to spray-drying catalyst compositions containing catalyst materials such as single-site catalysts together with alumoxane activator.
There is an ongoing need for methods of spray-drying catalyst compositions which result in product having good integrity and having higher activity and/or improved morphology, in particular, degree of sphericity and particle size uniformity. In particular, there is a need for such methods of spray-drying catalyst compositions, wherein the catalyst composition comprises a catalyst compound, a catalyst activator and a filler. The compositions and spray-drying methods of the present invention satisfy these needs.
The present invention provides catalyst compositions and methods of spray-drying such compositions. According to the present invention, the catalyst compositions comprise, in addition to a catalyst compound, an activator for the catalyst and a filler, one or more compound selected from among siloxanes, polyethylene glycols and crown ethers.
In accordance with the present invention, the inclusion of one or more compound selected from among siloxanes, polyethylene glycols and crown ethers in the catalyst compositions of the present invention results in spray-dried products which exhibit high degrees of uniformity of particle size and sphericity, i.e., extremely useful morphology, and provide excellent activity. The present invention is particularly effective where the catalyst compound does not include any cyclopentadiene ligands.
The invention further provides a process for producing an olefin polymer, which comprises contacting at least one olefin monomer under polymerization conditions with a product of spray-drying a catalyst composition as described above.